Re: [libvirt] [PATCHv3] Add unsafe cache mode support for disk driver

QEMU 0.13 introduced cache=unsafe for -drive, this patch exposes it in the libvirt layer. * Introduced a new QEMU capability flag ($prefix_CACHE_UNSAFE), as even if $prefix_CACHE_V2 is set, we can't known if unsafe

is supported. * Improved the reliability of qemu cache type detection. --- Updated patch based on Eric Blake's comments and rebased it to c4111bd0

+++ b/docs/formatdomain.html.in @@ -996,10 +996,15 @@ <li> The optional<code>cache</code> attribute controls the cache mechanism, possible values are "default", "none", - "writethrough", "writeback", and "directsync". "directsync" - is like "writethrough", but it bypasses the host page - cache. -<span class="since">Since 0.6.0</span> + "writethrough", "writeback", "directsync" (like + "writethrough", but it bypasses the host page cache) and + "unsafe" (host may cache all disk io and sync requests from

@@ -912,12 +914,16 @@ qemuCapsComputeCmdFlags(const char *help, else if (strstr(help, "-domid")) qemuCapsSet(flags, QEMU_CAPS_DOMID); if (strstr(help, "-drive")) { + const char *cache = strstr(help, "cache="); + qemuCapsSet(flags, QEMU_CAPS_DRIVE); - if (strstr(help, "cache=")&& - !strstr(help, "cache=on|off")) { - qemuCapsSet(flags, QEMU_CAPS_DRIVE_CACHE_V2); - if (strstr(help, "directsync")) + if (cache&& (p = strchr(cache, ']'))) { + if (memmem(cache, p - cache, "on|off", sizeof("on|off") - 1) == NULL) + qemuCapsSet(flags, QEMU_CAPS_DRIVE_CACHE_V2); + if (memmem(cache, p - cache, "directsync", sizeof("directsync") - 1)) qemuCapsSet(flags, QEMU_CAPS_DRIVE_CACHE_DIRECTSYNC); + if (memmem(cache, p - cache, "unsafe", sizeof("unsafe") - 1)) + qemuCapsSet(flags, QEMU_CAPS_DRIVE_CACHE_UNSAFE);